A plasma membrane preparation from rat adipose tissue and human erythrocytes has been prepared, which has many of the features of the glucose transport system in intact cell. The preferential uptake of H3- D-glucose when compared to C14-L-glucose retained on a millipore filter was used to mark "specific" D-glucose uptake. With the isolated plasma membrane prepations, it was observed that: 1) the D-glucose was taken up and released more rapidly than the L-isomer; 2) known inhibitors of glucose uptake inhibited the uptake of D-glucose and; 3) stereocompetitive sugars inhibited D-glucose uptake; 4) the D-glucose that was taken in the plasma membrane could be quantitatively eluted and found to be unchanged chemically; 5) the plasma membranes (in adipose tissue) on electron microscopy contained vesicles; 6) a "countercurrent" phenomenon could be demonstrated. Attempts to date to isolate the glucose transport system in the human erythrocyte preparation by using H3- and C14-dinitrofluorbenzene under conditions of the inhibition and acceleration of glucose transport (with the hope of demonstrating an enriched isotope ratio) have failed. In addition, attempts to solubilize the glucose transport system from the red cell membrane have been unsuccessful as well. Studies on insulin and adipose tissue cells are continuing. Using P32 as a marker of phosphopeptide metabolism, studies are underway to study labeling of phosphopeptides in various subcellular fractions of adipose tissue cells. It is hoped to localize the critical changes in phosphoprotein metabolism, and to define the chemical reactions involved, with particular reference to protein kinases and their molecular modifiers.